The present invention relates to a bonding wire for a semiconductor device adapted to be used for connection between a chip electrode of the semiconductor device and an external lead, and more particularly to such a bonding wire suitable for a ball bonding process.
It is known that a chip electrode of a semiconductor device is connected through a bonding wire such as Au wire to an external lead by melting a tip of the Au wire depending from an end of a capillary by means of an electrical torch to form a ball at the tip of the Au wire, pressing the ball against the chip electrode to bond together, then leading the Au wire to the external lead so as to form a loop, bonding the loop to the external lead, and finally cutting the Au wire.
In such a conventional bonding wire for a semiconductor device, however, a neck portion formed immediately above the ball is influenced by heat upon formation of the ball to relax a stress accumulated in the wire. Accordingly, a mechanical strength of the neck portion becomes lower than that of the base wire not influenced by heat. As the result, the neck portion is ruptured, or wire falling or wire sagging is generated during bonding work. Furthermore, in temperature cycle life test of products, a stress is generated by heat expansion and contraction due to repeated temperature change, and the stress is concentrated at the neck portion, causing a problem that the rupture of the neck portion is easily generated.
Meanwhile, in recent years, high-density mounting of LSI has accompanied a marked tendency to provide a multiplicity of pins. In this circumstance, it is demanded to reduce a diameter of the bonding wire and thereby reduce a bonding pitch.
However, as the neck portion of the aforementioned bonding wire is easy to rupture, it is impossible to reduce the diameter of the bonding wire, and the above demand cannot accordingly be met.